Level-crossing Experiments Research Articles

From Röntgen to Ioffe, from Giessen to Saint Petersburg — Relations between Russian and German physics

Two former professors of physics at Giessen university contributed significantly to the development of the Ioffe Institute: Wilhelm Conrad Rontgen as a teacher of Abram Ioffe, and Wilhelm Hanle, whose effect found various applications, e.g., in the spectroscopy of hot electrons in low-dimensional structures. A few examples will illustrate how topics of their scientific work found a continuation in the research activities at Giessen, but also in the collaboration between Giessen and Saint Petersburg. They range from sodium chloride, the old Rontgen/Ioffe material where we could prove the existence of an unusual isotope effect in nickel-doped crystals, over level-crossing experiments in gases, to GaAs/AlAs superlattices, where level-anticrossing spectroscopy of excitons reveals detailed information about recombination processes and interface quality. A short summary of the efforts to keep the traditionally close and good relations between Russian and German physics vital completes the report.

Level-crossing resonance spectra for bond-centred muonium in silicon

Abstract Previous avoided level-crossing experiments have revealed the microscopic structure of the paramagnetic anomalous muonium state in silicon: in addition to the axially symmetric hyperfine interaction along a (1, 1, 1) axis, distinct orientation-dependent superhyperfine interactions with first and second nearest neighbour 29Si nuclei have been observed. Here we report a theoretical study of the influence of further distant 29Si nuclei. Their contribution to the field dependence of the time-integrated longitudinal polarization function is investigated. The appearance of additional resonances is discussed and their locations as a function of field strength are calculated analytically by perturbation theory as well as numerically.

Hyperfine interaction versus strong laser field-optical Back–Goudsmit (Paschen–Back) effect

Strong laser perturbation of an atom with fine or hyperfine structure is analyzed in the context of a level-crossing experiment. The effect of sufficiently powerful, detuned, and/or spectrally broad light is to produce ‘‘hyperfine uncoupling,’’ which can be regarded as the optical Back–Goudsmit effect. It is easily understood in terms of an analogy between the level-crossing effect and double-slit experiment.

Level-crossing experiments by two-photon excitation

Complete orientation of the T172P3/2 (F=2) state by two-photon excitation allows Hanle-effect measurement in direct fluorescence as well as in the optical radiation cascade. The experiment provides estimations either of both the lifetimes of the involved excited states, or, if one of the lifetimes is reliably known, two independant determinations of the other. The measurements are reported on the background of other nonlinear Hanle-effect and level-crossing experiments.

Manipulation of level-crossing signals using narrow-band or pulsed laser excitation

Level-crossing experiments yielding Doppler-free signals are normally performed using a CW light source with a broad spectral distribution ("white" excitation), and the signals obtained are described by a well-known formula due to Breit. By using a single-mode dye laser or a pulsed laser for the excitation, strong modifications of level-crossing signals can be obtained. Profound changes in hyperfine structure crossing signals are demonstrated in experiments, performed in a cell, on the 9 2D3/2 state of 133Cs. Practical utilisation of unconventional excitation in level-crossing and optical double resonance spectroscopy is discussed.

Analysis of a level-crossing experiment on the 2 (3)P state of 3He.

We have used the theory presented by us in a recent paper to analyze a 1967 level-crossing experiment on the 2 $^{3}P$ state of $^{3}\mathrm{He}$ performed at the University of Michigan. Until now a consistent analysis of the experiment had not been possible because of inadequate development of the theory. The present analysis gives excellent agreement with the results of an atomic beam magnetic resonance experiment performed recently by us at Yale University. In fact we have used the combined data to give slightly improved results for four of the 11 relevant parameters. These four are the spin-antisymmetric contact hyperfine interaction constant [C'=-4327(69) MHz)], the 2 $^{3}P$ dipole hyperfine interaction constant [D=-28.145(21) MHz], the 2 $^{3}P$ tensor hyperfine interaction constant [E=-7.1353(38) MHz], and the orbital g factor [${g}_{L}$=0.999 828 6(20)]. .AE

On the Analysis of Periodic Signals in Spectroscopy by Photon Statistics

There are many experiments in spectroscopy in which some quantity is swept as a linear function of time. For instance, the frequency is swept when a spectrum is recorded, the magnetic field is swept in a level-crossing experiment, etc. If the intensity of the resulting light beam is small the detected signal has a large nose component. One can reduce noise by repeating the experiment periodically and using a multichannel signal analyzer to process the signal and obtain the information contained in it.

Error optimization in the detection of level crossing through the measurement of n^(2)(T)

Equations for calculation of the crossing point determination error and the signal width error in level-crossing experiments are generalized when the normalized second-order factorial moment of the fluorescence obtained is measured. To minimize the magnitude of these errors we study the behavior of these values on varying the magnetic field sweep interval, the counting time, and the mean fluorescence intensity.

Computer Simulation of Level-Crossing Detection by Conventional and Photon Correlation Techniques

Abstract We simulate by means of computer the signals obtained in a level-crossing experiment, when the detection is made by multichannel sampling and photon correlation techniques applied to the fluorescence intensity as a function of time. From the simulated signals we study the errors with which the crossing field and width of the signal are obtained, and we compare the results obtained by both techniques.

Limited spin diffusion towards quadrupolar relaxation centers in 1,8-dichlorooctane

The non-exponentiality of proton spin—lattice relaxation in polycrystalline 1,8-dichlorooctane is shown in Zeeman—quadrupole level-crossing experiments at various frequencies. An adequate description or magnetization recovery is obtained in a model of limited spin diffusion of protons towards fast relaxing chlorine quadrupolar centers. The magnitude of the diffusion coefficient is of the order 10 −16 cm 2 s .

Hanle lifetime measurements of SrI 1P 1 and CaI 1P 1 levels excited by a neutral beam of 1 1S 0 helium atoms

A 0.8 keV He(1 1S 0) beam was used to coherently excite the 1P 1 levels of Sr and Ca targets. The coherence appears as an alignment of the excited state with respect to the beam axis. We report here the results of a Hanle measurement, or a zero-field level-crossing experiment, performed on these coherently excited levels. The radiative lifetimes of the SrI 1P 1 and CaI 1P 1 levels were measured to be 4.7 ns and 5.3 ns, respectively. These values are in good agreement with conventional Hanle measurements.

Level-crossing study of the hyperfine structure of lithium

The method of level-crossing spectroscopy has been employed to measure the hyperfine interaction constants and the lifetimes of the $2^{2}P$ and $3^{2}P$ states of $^{7}\mathrm{Li}$. The parameters for the ${P}_{\frac{3}{2}}$ states were obtained from a conventional level-crossing experiment; it was also possible to measure the magnetic dipole hyperfine structure constant $A$ for ${P}_{\frac{1}{2}}$ states by using a newer method (similar to level crossing) called the method. With these techniques, it was possible to measure $A$ for the $2^{2}P_{\frac{3}{2}}$, $3^{2}P_{\frac{3}{2}}$, and $3^{2}P_{\frac{1}{2}}$ states of $^{7}\mathrm{Li}$. These measurements, together with the measurement of $B$ for the $3^{2}P_{\frac{3}{2}}$ state, made it possible to infer the nuclear quadrupole moment of $^{7}\mathrm{Li}$. In order to check the consistency of the $A$ values obtained from the decoupling runs, data were taken (using the decoupling method) for $A$ for the $2^{2}P_{\frac{1}{2}}$ and $3^{2}P_{\frac{1}{2}}$ states of $^{6}\mathrm{Li}$. In addition to the hyperfine data, the lifetimes for the $2^{2}P$ and $3^{2}P$ states were also obtained. The results are: ${A}_{\frac{3}{2}}(^{7}\mathrm{Li}2^{2}P)=\ensuremath{-}2.95(4)$ MHz, ${A}_{\frac{3}{2}}(^{7}\mathrm{Li}3^{2}P)=\ensuremath{-}1.036(16)$ MHz, ${A}_{\frac{1}{2}}(^{7}\mathrm{Li}3^{2}P)=13.7(12)$ MHz, ${A}_{\frac{1}{2}}(^{6}\mathrm{Li}3^{2}P)=5.3(4)$ MHz, ${A}_{\frac{1}{2}}(^{6}\mathrm{Li}2^{2}P)=17.8(3)$ MHz, $B(^{7}\mathrm{Li}3^{2}P)=\ensuremath{-}0.094(10)$ MHz, $\ensuremath{\tau}(2^{2}P)=26.4(8)$ nsec, $\ensuremath{\tau}(3^{2}P)=203(8)$ nsec, and $Q(^{7}\mathrm{Li})=\ensuremath{-}59(8)$ mb.

A level-crossing experiment in the 6s6p 1P 1-state of 173Yb with additional optical pumping of the ground state

The 6 1P 1 state of 173Yb has been investigated by the level-crossing technique with additional optical pumping of the ground state. With the results of this experiment a long existing uncertainty in the hfs coupling constants could be removed.

Untersuchung von Level-Crossing-Signalen an schnellen He-Atomen in inhomogenen Magnetfeldern / Investigation of Level-crossing Signals on High-velocity He-atoms in Inhomogeneous Magnetic Fields

Abstract In level-crossing experiments on high-velocity atoms, the shape of the observed signals depends sensitively on inhomogeneities of the applied magnetic field. With regard to the interpretation of such signals, we investigated the magnetic-field dependence of He I-fluorescence light excited by He-ion-He-atom collisions. Due to the inhomogeneity of the applied magnetic field, the observed level-crossing signals have a distorted shape with an oscillating structure in the wings. Taking into account the motion of the excited atoms, the shape of the signals will be explained.

Orientation of Atoms by Collisions with Inclined Surfaces

We have measured large orientations for Ar II states excited by 300-keV Ar/sup +/ impact on solid Cu surfaces at grazing incidence. We report circulary polarized light fractions of up to 76% and interpret the excitation mechanism as an orbital-angular-momentum effect. As an application of this new excitation scheme, a zero-field level-crossing experiment is presented. (AIP)

Hyperfine constants in the 52P3/2state of85Rb

The results of a level-crossing experiment are reported. The hyperfine constants of the 5 2P3/2 state of 85Rb are a=24.99(1) and b=25.88(3). These values are compared with those from a previous optical double resonance experiment. When radiative shifts are carefully taken into account in the ODR measurements, very good agreement is found.

Isotope shift of 47-day ^203Hg†

An improved value of the 203Hg–198Hg isotope shift in the 2537 A 3P1–1S0 line of mercury was determined from emission spectroscopy, with mass-separated samples, and from absorption spectroscopy with unenriched pile-produced isotope. The spectroscopic data were analyzed to yield the isotope shift by use of precise hfs interaction constants that we obtained previously from a level-crossing experiment. The new value for the 203Hg–198Hg isotope shift is IS(203–198) = 0.392 ± 0.006 cm−1; 203Hg lies at the lower-wave-number side. The experiment demonstrates the advantages of absorption spectroscopy for samples of low isotopic purity. The application of this technique to work with small samples is also discussed.

Fine Structure, Hyperfine Structure and Lamb Shift Measurements by the Beam-foil Technique

A survey on high resolution experiments with atomic systems prepared by the beam-foil or beam-gas interaction is presented. RF-resonance, field-quenching, quantum-beat and level-crossing experiments are described in elementary terms whereas more advanced theoretical techniques are sketched for quantum beats in an appendix.

Zur Messung von Vorzeichen atomarer Aufspaltungskonstanten bei Verwendung von Hochfrequenz- und Level-Crossing-Techniken / On the measurement of signs of atomic splitting constants using radio frequency and level-crossing techniques

In radiofrequency and level-crossing experiments the sign of atomic splitting constants (e. g. hfsconstants, gJ-values, tensor polarizabilities) can often be measured only under special experimental conditions. Some general features of these conditions are discussed starting from transformation properties of the atomic hamiltonian. In particular, the dependenec of level-crossing signals on the signs of atomic splitting constants is analyzed.

High-field level-crossing and Stark studies of the A 2Σ+ state of OD

We have carried out a high-field level-crossing experiment on the ν = 0, N=1, J=3/2 ot the OD A 2Σ+ state. A precise measurement of the magnetic fields at which three crossovers are observed permits a determination of the three hyperfine constants b = 110.4 ± 2.6 MHz, c = 22 ± 14 MHz, and eQq = 0.09 ± 0.05 MHz (3σ). In addition, we have applied a static electric field parallel to the magnetic field and observed a shift in the location of the high-field level crossings from which we calculate the dipole moment of this excited state to be 1.72 ± 0.10 D (3σ). A comparison of these structural parameters is made with ab initio calculations.